Combustion catalyst and process for using same

ABSTRACT

A unique class of copper zeolite combustion catalysts which are both highly siliceous and contain an extraordinary amount of zeolitic divalent copper cations which are prepared by ion exchanging the predominantly alkali metal cation form of ZSM-5 type zeolites with divalent copper cations and subjecting the resulting compositions to rigorous oxidation.

RELATED APPLICATIONS

This application is a division of pending application Ser. No. 864,835filed Dec. 27, 1977, now U.S. Pat. No. 4,170,571 issued Oct. 9, 1979.

The present invention relates to a novel zeolite composition of mattersuitable for use in catalyzing the combustion of carbonaceous substratesand to the combustion process per se. More particularly, the inventionconcerns a novel zeolitic copper aluminosilicate and its use as acatalyst in the oxidative combustion of hydrocarbons and carbon monoxidein pollution abatement processes.

It has heretofore been proposed to utilize a variety ofcopper-containing compositions to catalyze the oxidative combustion ofcarbonaceous substances in the vapor phase. Copper oxide, either aloneor in combination with transition metal oxides, has long been employedas a catalyst in the oxidation of hydrocarbons. More recently thedivalent copper ion in the form of a zeolitic cation has been found tohave significant catalytic activity in the conversion of carbon monoxideto carbon dioxide. In U.S. Pat. No. 3,346,328, for example, it isproposed to use as the catalyst for treating internal combustion engineexhaust gases, a Cu⁺⁺ exchanged zeolite such as zeolite Y which has CuOloaded or held interstitially in its pore system. Since the copper ionis found to play an important part in hydrocarbon conversion and copperoxide is an influential factor in carbon monoxide conversion, theactivity of the catalyst is optimized for a particular exhaust gas byvarying the proportion of zeolitic CU⁺⁺ cations and impregnated CuO.

When it is desired to maximize the hydrocarbon combustion activity ofzeolite base catalysts, the number of zeolitic copper cations has, priorto the present invention, been limited by the number of AlO₄ ⁻tetrahedra per unit cell of the zeolite crystal. This followsnecessarily from the fact that zeolite cations exist in the zeolitestructure only for the purpose of electrovalently balancing theframework tetrahedra. In zeolites which have molar SiO₂ /Al₂ O₃ ratiosless than about 10, little difficulty is experienced in exchanging asufficient number of the original monovalent zeolite cations to obtainan adequate concentration of divalent copper cations for catalysispurposes. Such alumina-rich zeolites, however, exhibit a much strongeraffinity for water and other relatively polar molecules than for theweakly polar or non-polar hydrocarbon and CO substrates being oxidized.As a result, the catalytically active CU⁺⁺ sites of the zeolite soonbecome "poisoned" by the oxidation products and the rate of the desiredcombustion reaction is severly decreased unless the reaction system ismaintained at prohibitively high temperatures or the catalyst isdesorbed at impractically frequent intervals.

Advances in zeolite synthesis techniques, principally the substitutionof organic amine-type cations for some or all of the alkali metalcations in conventional reaction gels, have resulted in the formation ofzeolites having SiO₂ /Al₂ O₃ molar ratios in the range of greater than10 up to 300 or greater, i.e. values at which the AlO₄ ⁻ content appearsto be crystallographically insignificant. Also improved methods forextracting AlO₄ ⁻ tetrahedra from alumina-rich zeolites to createsiliceous zeolite products have been developed. It is generally foundthat when the SiO₂ /Al₂ O₃ molar ratio exceeds about 20, there is amarked decrease in the hydrophilic nature of the zeolite and acommensurate increase in its organophilic nature. Accordingly, highlysiliceous zeolites per se have been proposed as catalysts in processesin which organic molecules of low polarity are converted to morestrongly polar products. Processes of this type are disclosed, forexample, in U.S. Pat. No. 3,728,408 issued to M. A. Tobias on Apr. 17,1973.

In the case of the more refractory hydrocarbons, however, the catalyticactivity of the highly siliceous zeolite framework is not great enoughto accomplish complete oxidative combustion using reasonable conditionsof space velocity and temperature. Moreover, attempts to introducecatalytically effective amounts of Cu⁺⁺ cations into these alumina-poorzeolites have been generally unsuccessful for several reasons.

Firstly, the only known sources of copper cations suitable forintroduction into the zeolite lattice by aqueous ion-exchange techniquesare the water soluble salts of copper in which the copper cation isdivalent. The tendency of each divalent Cu⁺⁺ cation is to balance theelectrovalence of two AlO₄ ⁻ tetrahedra, each formerly associated with asingle monovalent cation. Thus, the relatively few AlO₄ ⁻ tetrahedra inthe zeolite are essentially halved in number insofar as providing acation site to be occupied by Cu⁺⁺ cations is concerned. This places apremium on the use of zeolites with a relatively low SiO₂ /Al₂ O₃ molarratio with the consequence that the essential hydrophobic ororganophilic property cannot be maximized in the catalyst composition.

Secondly, upon dehydration, i.e. activation of Cu⁺⁺ exchangedhigh-silica zeolites such as acid-extracted zeolite Y, it is observedthat there is a spontaneous conversion of the Cu⁺⁺ cations to themonovalent form and the formation of an equal number of cation sitesoccupied by protons. Not only are the monovalent Cu⁺ cations notequivalent to Cu⁺⁺ cations with respect to combustion catalysis, butalso there is a marked tendency for the monovalent copper cations to bereduced to elemental copper and consequent further loss of catalyticactivity. Moreover, the Cu⁺ zeolite cation readily forms a bidentatecomplex with two molecules of CO. One of the CO ligands is readilyremovable, but the resulting monodentate is extremely stable andrequires heating at 200° C. under vacuum for dissociation.

There has now been discovered a unique class of copper zeolites whichare both highly siliceous and contain an extraordinary amount ofzeolitic divalent copper cations. The very high selectivity andhydrophobicity of these catalyst compositions make them ideally suitedfor use in the oxidative combustion of even the most refractory ofhydrocarbons. These zeolite compositions have the crystal structure ofthe ZSM-5 type of aluminosilicates, at least 80% of the AlO₄ ⁻tetrahedra thereof being associated with, i.e. electrovalentlyneutralized by a zeolite divalent copper cation. The composition in thedehydrated state can be expressed empirically in terms of mole ratios ofoxides as:

1.6-2.0 Cu⁺⁺ O:0-0.2 M₂ /_(n) O:Al₂ O₃ :20-100 SiO₂ wherein "M" is atleast one cation other than Cu⁺⁺, said composition having acharacteristic X-ray powder diffraction pattern containing at least thefollowing d-spacings:

                  TABLE I                                                         ______________________________________                                        Interplanar Spacing, d(A)                                                                      Relative Intensity, I/I.                                     ______________________________________                                        11.1 ± 0.2    S                                                            10.0 ± 0.2    S                                                            7.4 ± 0.15    W                                                            7.1 ± 0.15    W                                                            6.3 ± 0.1     W                                                            (6.04 ± 0.1   W                                                            (5.97                                                                         5.56 ± 0.1    WW                                                           5.01 ± 0.1    W                                                            4.60 ± 0.08   W                                                            4.25 ± 0.08   W                                                            3.85 ± 0.07   VS                                                           3.71 ± 0.05   S                                                            3.04 ± 0.03   W                                                            2.99 ± 0.02   W                                                            ______________________________________                                         VS = Very Strong; S = Strong; W = Weak                                   

These values were determined by standard techniques. The radiation wasthe K-alpha doublet of copper, and a scintillation counter spectrometerwith a strip chart pen recorder was used. The peak heights, I, and thepositions as a function of 2 times theta, where theta is the Braggangle, were read from the spectrometer chart. From these, the relativeintensity values, 100 I/Io where Io is the intensity of the strongestline or peak, and d(obs.), the interplanar spacing in A, correspondingto the recorded lines, were calculated.

Preferably, the SiO₂ /Al₂ O₃ molar ratio of the present zeolitecompositions is from about 40 to 85.

The class of zeolites referred to herein as ZSM-5 type includes not onlyZSM-5 itself but also ZSM-11, ZSM-21 and other similarly behavingmaterials. U.S. Pat. No. 3,702,886 describing and claiming ZSM-5 isincorporated herein by reference.

ZSM-11 generally corresponds to the empirical formula:

    0.9±0.3 M.sub.2 O:Al.sub.2 O.sub.3 :20-90 SiO.sub.2 :Z H.sub.2 O

where M is at least one cation, n is the valence of M and Z is 6 to 12in the "as produced" zeolite. The preferred M is alkali metal or alkylammonium or a mixture thereof, preferably sodium or tetraethylammonium.ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, theentire contents of which are incorporated herein by reference.

In a preferred synthesized form, the ZSM-21 zeolite has a formula, interms of mole ratios of oxides and in the anhydrous state as follows:

    (0.4-2.5)R.sub.2 O:0.1-0.5 M.sub.2 O:Al.sub.2 O.sub.3 :xSiO.sub.2

wherein R is an organic nitrogen containing cation, especially a cationderived from ethylenediamine, pyrrolidine or 2-(hydroxyalkyl)trialkylammonium compounds, wherein alkyl is methyl, ethyl or acombination of the two, M is an alkali metal, especially sodium, and xis from greater than 10 to about 50.

Reference is made to U.S. Pat. No. 3,756,942, for a more completedescription of the various specific catalysts in the ZSM-5 class and formethods of preparing such.

In general, some zeolite molecular sieves have in the past beencharacterized as shape selective, that is, having pore openings so sizedand shaped as to admit substantially only normal paraffins into theirinternal pore structure, or non-shape selective or large pored, that ishaving pore openings so sized and shaped as to admit substantially anyconfiguration of organic compound into their internal pore structure. Ithas become usual in this art to refer to shape selective zeolites asthose havig pore openings of about 5 to 7 Angstrom units or less and tonon-shape selective zeolites as those having pore openings of about 11Angstrom units or more.

The ZSM-5 type of zeolite molecular sieve seems to differ from theseother materials in that it is shape selective not only for normalparaffins but for slightly branched, e.g. methyl substituted, paraffinsas well.

The ZSM-5 type of zeolite also appears to be unique in its ion exchangeproperties with respect to aqueous ion exchange media containingdivalent copper cations. As is evident from the empirical formula setforth above, if the zeolite Cu⁺⁺ cations known to be present in thepresent zeolite compositions were associated with the AlO₄ ⁻ tetrahedrain the conventional manner, they would represent from 160 to 200% of thetheoretical maximum. Although cation populations somewhat in excess ofthe theoretical maximum can be attributed to analytical tolerances andimpurities in the zeolite composition, other explanations must beprovided for values which appear to deviate from the norm as greatly asin the present compositions.

Although not wanting to be bound by any particular theory, the availableevidence suggests that the divalent Cu⁺⁺ zeolitic cations in the presentzeolites in the as ion-exchanged and unactivated state, are largelyhydroxylated cations and are bonded to the zeolite structure through asingle copper-to-zeolite bond, i.e. CuOH⁺. This is supported by the factthat the copper cations in this state do not react with CO as monovalentCU⁺ zeolite cations are known to do. Also upon vacuum activation attemperatures above about 300° C., these putative hydroxylated Cu⁺⁺cations are converted to Cu⁺ zeolite cations as evidenced by theirreactivity with CO to form the bidentate complex: ##STR1##

In the unactivated, as-ion-exchanged state, the copper cations which arenot present as divalent hydrated species have been established to beessentially monovalent CU⁺ zeolitic cations by ESR techniques inconjunction with CO reactivity studies. Thus upon dehydration(activation) of the copper exchanged zeolite there is created a form inwhich substantially all of the copper cations are monovalent and each isassociated with a single AlO₄ ⁻ tetrahedron. To obtain the requireddivalent Cu⁺⁺ cation form it is found that when the monovalent Cu⁺ formis contacted at ambient room temperature (22° C.) with a strong oxidantsuch as chlorine, ozone or NO₂, preferably NO₂ or a mixture of NO₂ andO₂, an essentially stoichiometric conversion to the Cu⁺⁺ form occurs. Itcan be surmised that these copper-containing cations are, at least inthe case where NO₂ is the oxidant, somewhat analogous in structure tothe hydroxylated divalent copper cations of the unactivated precursorwherein the NO₂ moiety functions in a similar manner to the hydroxylgroup in that case. The same results are obtained in the NO₂ plus O₂treatment is simultaneous with the activation (dehydration) of theas-exchanged form of the zeolite.

Accordingly, the present compositions contain copper cations which areboth divalent, zeolitic in nature and present in concentrations per AlO₄⁻ tetrahedra approximately 160 to 200 percent of that which are obtainedby conventional ion exchange of other zeolite compositions.

In preparing the compositions of the present invention it is essentialthat the ZSM-5 type zeolite starting material has at least 80, andpreferably at least 90 percent of its AlO₄ ⁻ tetrahedra associated withalkali metal, preferably lithium, potassium or sodium cations. It isfound that even if the requisite number of AlO₄ ⁻ are associated withexchangeable cations other than alkali metal, e.g. H⁺, Ca⁺⁺, NH₄ or Ba,the compositions of the present invention are not produced. It can betheorized that the unique crystal structure of the ZSM-5 type zeolitetogether with the basic (as opposed to acidic) character of the sodiumcation sites may create localized pH conditions favorable to theformation of hydroxylated divalent copper cations, but the validity ofthis proposition has not been established with certainty.

As disclosed in U.S. Pat. No. 3,702,886, the zeolite species can besynthesized in a form which the zeolitic cations are a mixture oftetrapropylammonium and sodium cations. The concentration oftetrapropylammonium cations in the as-synthesized product isapproximately proportional to their relative concentration in thereaction gel with respect to the sodium cations also present. Thetetrapropylammonium cations, at least in part because of molecular sizeconsiderations, cannot be ion exchanged from the crystal lattice.However, where it is necessary to insert sodium cations into at leastsome of the sites occupied by the tetramethylammonium species thetechnique for removing organic cations described in U.S. Pat. No.3,853,743, A. B. Schwartz, can be employed. This procedure comprisesheating the organic cation-containing zeolite at a temperature betweenabout 500° F. and about 1,000° F. in an atmosphere of ammonia ormixtures thereof with nitrogen for a period of 10 minutes to 10 hours.These conditions prevent loss of crystallinity and preserve the cationicsites in the zeolite which can then become occupied by sodium cationsupon conventional ion exchange with an aqueous sodium salt solution. Thedisclosure of U.S. Pat. No. 3,853,743 is incorporated herein byreference.

A ZSM-5 type zeolite, as defined herein, can be prepared free of organiccations and having substantially all sodium cations by the hydrolthermalconversion at 80° C., to 210° C., for 40 to 200 hours under autogeneouspressure of a reaction gel having a composition in terms of mole ratiosof oxides within the following range:

SiO₂ /Al₂ O₃ =10 to 100

Na₂ O/SiO₂ =0.04 to 1.5

H₂ O/Na₂ O=20 to 600

It will be understood, however, that this synthesis process is not apart of the present invention. It is described in greater detail inco-pending application Ser. No. 655,065 filed Feb. 4, 1976, thedisclosure of which is incorporated herein by reference in its entirety.

The ion-exchange procedure for transforming the sodium cation form ofthe ZSM-5 type starting materials defined hereinbefore is readilyaccomplished using commonly available copper salts such as CuCl₂, CuSO₄and cupric acetate in an aqueous medium. A satisfactory procedurecomprises contacting at reflux temperature the starting zeolite with 25ml. per gram at an aqueous solution containing the cupric salt in aconcentration of 0.4 mole per liter of water. Contact is maintained forabout 3 hours, and then the procedure is repeated two more times usingfresh ion exchange medium. In washing the final zeolite product withdistilled water to remove extraneous salts, care should be taken toavoid overwashing and consequent H⁺ exchange of the coppercation-containing product. Advantageously the pH of the washing watershould not be lower than 6.3.

Conversion of the as-exchanged copper ZSM-5 type zeolite to the novelcomposition of the present invention is accomplished by contacting samewith a strong oxidant, preferably NO₂ alone or in an admixture withoxygen, either during or after activation (dehydration) to removeadsorbed water. The relative proportions of oxidant NO₂ and zeolite isnot a narrowly critical factor, but at least one oxidant molecule shouldbe present for each cation site of the zeolite. As a practical matter alarge stoichiometric excess of oxidant will oridinarily be used. It isfound that an air atmosphere containing 20 mole percent NO₂ is ideal forthe purpose. Temperatures of from 20° C. to 375° C. have been found tobe satisfactory: Pressure conditions are not a critical factor.

It is preferred to contact the zeolite with the oxidant after the bulkof the adsorbed water is removed but before total dehydration occurs.This procedure suppresses the formation of intermediate Cu⁺ cations andretains the initially present hydroxylated Cu⁺⁺ cations in the divalentstate. Upon dehydroxylation of the original CuOH⁺ cation species and theformation of Cu⁺ cations, it is possible, however, to again form thedivalent copper cation species by oxidation, preferably by contact withNO₂ at ambient room temperature.

The preparation and utilization of the compositions of the presentinvention are illustrated by the following examples:

EXAMPLE 1

A reaction mixture was prepared by dissolving 1.2 g. of NaOH and 0.6 gNaAlO₂ (30.2 wt.-% Na₂ O, 44.1 wt.-% Al₂ O₃, 24.3 wt.-% H₂ O) in 25 g.of hot H₂ O and adding with stirring to 44 g. of aqueous colloidalsilica sol (30 wt.-% SiO₂) in 100 g. of H₂ O. The overall molar oxidecomposition was:

    6.5Na.sub.2 O.Al.sub.2 O.sub.3.80SiO.sub.2.3196H.sub.2 O.

The reactant mixture was placed in a polytetrafluoroethylene-linedautoclave and maintained at about 200° C. and autogenous pressure forabout 72 hours. The solid product was separated by filtration, washedwith H₂ O and dried at 110° C. Chemical analysis of a sample of thisproduct gave the following composition: 1.9 wt.-% Na₂ O, 2.7 wt.-% Al₂O₃, 89.2 wt.-% SiO₂, 5.5 wt.-% H₂ O. The molar composition was, in termsof oxides:

    1.19Na.sub.2 O.Al.sub.2 O.sub.3.57.2SiO.sub.2.11.8H.sub.2 O.

A portion of the product was activated at 350° C. in vacuum for about 16hours in a McBain-Bakr gravimetric adsorption system. The activatedzeolite adsorbed 8.2 wt.-% O₂ at 750 torr, -183° C.; 3.9 wt.-% isobutaneat 750 torr, 23° C.; 0.3 wt.-% neopentane at 750 torr, 23° C.; and 7.7wt.-% H₂ O at 20 torr, 23° C. The X-ray powder diffraction pattern ofthe zeolite product is set forth in Table II, below:

                  TABLE II                                                        ______________________________________                                        d-A              I                                                            ______________________________________                                        11.2             15                                                           10.16            24                                                           9.82             4                                                            9.02             4                                                            7.44             1                                                            7.02             1                                                            6.66             1                                                            6.37             2                                                            5.98             4                                                            5.72             3                                                            5.57             2                                                            5.37             1                                                            5.10             1                                                            5.01             3                                                            4.60             1                                                            4.51             1                                                            4.37             4                                                            4.08             1                                                            4.00             4                                                            3.85             41                                                           3.82             27                                                           3.74             15                                                           3.72             10                                                           3.65             5                                                            3.60             1                                                            3.45             6                                                            3.25             2                                                            3.19             2                                                            3.15             1                                                            3.06             3                                                            3.00             4                                                            2.95             1                                                            ______________________________________                                    

The non-activated portion of the zeolite product was slurried for 3hours at reflux temperature in an aqueous solution containing 0.4 moleof CuCl₂ per liter of water. Sufficient solution was used to provide0.01 mole of CuCl₂ per gram of zeolite present. At the end of the 3 hourperiod, the zeolite was isolated by filtration and the procedurerepeated two more times. The copper ion-exchanged product was washedchloride-ion free using distilled water having a pH of 6.3, and dried inair at 100° C. Conversion of the Cu⁺ cations present to zeolite Cu⁺⁺containing cations was accomplished by passing a stream of dry aircontaining 20 mole percent NO₂ over the zeolite for a period of 2 hours.The final dehydrated composition in terms of mole ratios of oxides was:

    1.86Cu.sup.++ O:0.20Na.sub.2 O:Al.sub.2 O.sub.3 :SiO.sub.2.

EXAMPLE 2

The Cu⁺⁺ ZSM-5 type zeolite prepared as in Example 1 was compared with aconventional commercial combustion catalyst in toluene combustion. Thecomparison catalyst was a copper carbonate--manganese carbonate mixturesupported on a Bentonite clay basis. Upon heating the copper carbonatedecomposes to CuO. The chemical composition of the catalyst in terms ofoxides was:

    ______________________________________                                                     Wt.-%                                                            Component    Volatile-Free Basis                                              ______________________________________                                        Al.sub.2 O.sub.3                                                                           3.3                                                              SiO.sub.2    9.9                                                              Na.sub.2 O   0.6                                                              MnO          37.7                                                             CuO          47.7                                                             CaO          0.2                                                              Fe.sub.2 O.sub.3                                                                           0.6                                                              ______________________________________                                    

The zeolite catalyst composition contained about one tenth of the numberof active cation sites as the commercial nonzeolite catalyst. Bothcatalyst comositions were pelleted and placed in quartz tubular reactors2.5 cm. ID×30 cm. long equipped with variable heating means andthermocouples to measure the temperature at various points in thecatalyst mass. A gas stream composed of eight parts by volume helium,two parts oxygen and 0.05 parts toluene was passed through each reactorat a space velocity of 10,000 hr.⁻¹. The combustion results are shown intubular form below. Unless otherwise indicated the catalyst massessustained adiabatic combustion at the temperature indicated.

                  TABLE III                                                       ______________________________________                                        Minimum Preheat Temp.,        Commercial                                      °C. Required:                                                                          Cu.sup.++  ZSM-5 Type                                                                       Catalyst                                        ______________________________________                                        For Fresh Catalyst to                                                                         150           150                                             Initiate Combustion                                                           For Complete Combustion                                                                       220           220                                             by Fresh Catalyst                                                             To Initiate Combustion                                                                        150           180                                             After Catalyst Exposed                                                        to 100% Humidity for                                                          1.0 Hours                                                                     For Complete Combustion                                                                       220            220.sup.a                                      After Catalyst Exposed                                                        to 100% Humidity for                                                          1.0 Hours                                                                     To Initiate Combustion                                                                        150           230                                             by Catalyst Exposed                                                           to 800° C. for 4.0 Hours                                               For Complete Combustion                                                                        250.sup.a     360.sup.a                                      by Catalyst Exposed to                                                        800° C. for 4.0 Hours                                                  ______________________________________                                         .sup.a No longer sustained adiabatic combustion.                         

EXAMPLE 3

The catalytic activity of the zeolite catalyst of Example 1 was comparedwith that of a ZSM-5 zeolite catalyst which was prepared by ion-exchangeof a starting zeolite which contained less than 80 percent of itsalumina tetrahedra associated with sodium cations. The ZSM-5 zeolite wasprepared as follows: Twenty grams of NaOH and 24 grams of sodiumaluminate (NaAlO₂) were dissolved in 150 grams of water. A secondsolution was prepared by dissolving 106 grams of tetrapropylammoniumbromide in 150 grams of water. The first solution was then added to andblended with a slurry of 1760 grams of aqueous silica sol (30 wt.-%SiO₂) in 700 grams of water, and finally the second solution was addedand blended well. The resulting gel having a composition in terms ofmole ratios of oxides of:

    1.8TPA.sub.2 O:3.5Na.sub.2 O:Al.sub.2 O.sub.3 :80SiO.sub.2 :1150H.sub.2 O

was then digested at 200° C. for about 77 hours and the crystallinezeolite product isolated by filtration, washed and dried. Theas-synthesized product had a composition in terms of mole ratios ofoxides on an anhydrous basis:

    0.75Na.sub.2 O:0.25TPA.sub.2 O:Al.sub.2 O.sub.3 :80.6SiO.sub.2

The composition was calcined at 600° C. to decompose the organic cationsand then ion-exchanged using the following procedure: To a solution of6.72 grams (10 fold excess) of cupric chloride in 250 ml. distilledwater was added 10 grams of calcined ZSM-5 zeolite. After refluxing withstirring for 3 hours the mixture was filtered, the solids returned tothe flask and the exchange repeated using fresh cupric chloridesolution. The filtered solids were washed once by stirring with waterfor 1 hour, then filtered and dried in racuo at 100° C. Analysis by "aa"showed 1.09 wt.-% Cu, 0.02 wt.-% Na and 6.0 wt.-% LOI at 1000° C., thusindicating a Cu⁺⁺ ion-exchange of 92 percent of theory.

Using essentially the same apparatus and technique set forth in Example2, it was found that the activity of the catalyst composition of Example1 resulted in 100% combustion of toluene to CO₂ at 300° C. in a reactionthat began initially at 150° C. In marked contrast, the comparisonzeolite catalyst prepared in this Example 3 did not initiate combustionuntil a temperature of 200° C. was reached, and resulted in a 63 percentoxidation to CO₂ at 350° C. Also significant amounts of hydrocarbondegradation products, principally benzene, were detected in the emissionfrom the reactor in the case of the comparison catalyst.

EXAMPLE 4

The catalyst of Example 2 was compared with a Cu⁺⁺ exchanged type-Yzeolitic catalyst in the combustion of ethane. The type-Y zeolite was asteam stabilized composition having the chemical composition (anhydrousbasis):

    0.04Na.sub.2 O:0.93CuO:Al.sub.2 O.sub.3 :31.4SiO.sub.2

and was prepared by conventional ion exchange using 13.4 g. CuCl₂ in 250ml. water (5-fold excess of Cu⁺⁺). Using essentially the same apparatusand techniques set forth in Example 2, it was found that the type-Ycatalyst at 350° C. converted 23 wt.-% of the ethane to CO₂, 5 wt.-% toCO and 1 wt.-% to ethylene. At 300° C. and otherwise under the sameconditions, the catalyst of Example 1 converted 40 wt.-% of the ethaneto CO₂, and produced no CO and only trace amounts of ethylene.

EXAMPLE 5

The Cu⁺⁺ ZSM-5 type zeolite prepared as in Example 1 was used to combusta variety of common organic solvents of widely varying structure. Theapparatus and procedure described in Example 3 were used with theexception that the concentration of solvent vapor was maintained below0.05 parts by volume, or sufficiently dilute as to preclude adiabaticcombustion. The results are shown in tubular form below. In no case wereproducts of partial combustion or coking observed.

                  TABLE IV                                                        ______________________________________                                                          Minimum                                                                       Temp. for                                                                     100%                                                                          Combustion Ignition Point                                   Solvent           (°C.)                                                                             (°C.)                                     ______________________________________                                        Toluene           380        190                                              Xylene            370        190                                              Methyl Ethyl Ketone                                                                             330        190                                              Methyl Isobutyl Ketone                                                                          370        140                                              Isopropanol       380        190                                              CELLOSOLVE Solvent                                                                              350        190                                              Methyl CELLOSOLVE Acetate                                                                       320        190                                              Mineral Spirits   340        210                                              ______________________________________                                    

What is claimed is:
 1. Process for oxidatively combusting a chemicalcompound selected from the group consisting of hydrocarbons, carbonmonoxide and oxygenated hydrocarbons which comprises contacting saidcompound in admixture with oxygen at a temperature of from 100° C. to450° C. with a copper zeolite having in the dehydrated state acomposition in terms of mole ratios of oxides as:

    1.6-2.0Cu.sup.++ 0:0-0.2M.sub.2/n O:Al.sub.2 O.sub.3 :20-100SiO.sub.2

wherein M is at least one cation other than Cu⁺⁺ having a valence of"n", said zeolite composition having a characteristic X-ray powderdiffraction pattern containing at least the d-spacings of Table I.